Selective recovery of neodymium from oxides by direct extraction method with supercritical Co₂containing TBP–HNO₃complex

A method for the direct extraction of a metal utilizing supercritical CO2 containing tri-n-butylphosphate (TBP)–HNO3 (TBP), which is the TBP solution of TBP–HNO3 complex, has been developed for the recovery of Nd from its oxide. This method was applied using a flow reactor to several oxides (Nd2O3, ZrO2, MoO3, and RuO2), and binary mixtures of the oxides (Nd2O3–ZrO2, Nd2O3–MoO3, and Nd2O3–RuO2). Neodymium (Nd) was extracted almost quantitatively from 0.01 mol Nd2O3 powder with supercritical CO2 containing TBP–HNO3 (TBP) at 313K and 12 MPa, while Zr, Mo, and Ru were hardly extracted from their oxides and remained in the reactor. Nd was extracted quantitatively and selectively also from the binary mixtures of the oxides. From these results, it is found that the supercritical CO2 extraction process using TBP–HNO3 (TBP) as reactant is feasible for the selective recovery of lanthanides directly from the various oxide mixtures.